sub marsExploration {
    my $s = shift;
    
    my @arr = split("", $s);
    my $cnt = 0;
    for (my $i = 0; $i <= scalar(@arr) - 1; $i += 3) {
        $cnt++ if ($arr[$i] ne "S");
        $cnt++ if ($arr[$i+1] ne "O");
        $cnt++ if ($arr[$i+2] ne "S");
    }
    
    return $cnt
}

const SOS = (l: number) => 'SOS'.repeat(l);
const SBD = (l: number, cb: (i: number) => string) => Array(l).fill('').map((_, i) => cb(i)).join('');
function marsExploration(s: string): number {
    let recieved_signal = s;
    let expected_signal = SOS(s.length / 3);
    let differen_signal = SBD(s.length, i => recieved_signal[i] != expected_signal[i] ? 'X' : ' ');

    console.log('Expected signal:', expected_signal)
    console.log('Recieved signal:', recieved_signal)
    console.log('Difference:     ', differen_signal)

    return differen_signal.split('').reduce((p, c) => c == 'X' ? p + 1 : p, 0)
}

public static int marsExploration(String s) {
  // Write your code here
  int diff = 0;
  for (int i = 0; i < s.length(); i++) {
    if ((i % 3 == 0 || i % 3 == 2) && s.charAt(i) != 'S') {
      diff++;
    } else if (i % 3 == 1 && s.charAt(i) != 'O') {
      diff++;
    }
  }
  return diff;
}

int marsExploration(string s) {
   int result = 0;
    string base = "SOS";
    for(int i = 0; i < s.size(); i++) if(s[i] != base[i%3]) result++;
    return result;
}

def marsExploration(s):
    c=0
    for i in range(0,len(s)//3):
        if s[0+3*i]!='S':
            c+=1
        if s[1+3*i]!='O':
            c+=1
        if s[2+3*i]!='S':
            c+=1
        
    return c